Dark sky great backdrop for tonight's meteor shower

Get ready for one of the best shows of the year: the annual Geminid meteor shower.

This year, the sky will be good and dark because the moon will be out of sight. And if you are skywatching from the even-darker countryside, you may see 50 to 75 meteors per hour this week. Peak hours will be from midnight to early-morning twilight Friday, Dec. 14.

This show is called the Geminid meteor shower because all the meteors appear to be streaming from the general direction of the constellation Gemini, the twins, which is in the western half of the sky in the early morning.

But don't restrict your viewing to only that part of the sky. Meteors will be visible throughout the heavens. For best viewing, recline in a lawn chair and let your eyes wander. No binoculars or telescopes are required; you want a wide view of the sky.

Meteor showers occur when Earth, orbiting the sun, runs into a debris trail of dust and small pebbles. In most meteor showers, the debris is left behind by a passing comet. Not so with the Geminids. That debris trail was left by an asteroid astronomers call 3200 Phaethon.

The asteroid, discovered in 1983, has a diameter of about 3 miles. It has a highly elliptical orbit and swings by our part of the solar system every year and a half. Each time it passes, it refreshes the debris trail.

The debris particles are called meteoroids, and most are smaller than a thumbnail. They slam into our atmosphere 50 to 80 miles high at speeds that can exceed 40 miles per second. They burn up in our atmosphere due to air friction. The streaks we see are caused by columns of air becoming chemically excited by the meteoroids ripping though them.

Meteor showers are best seen after midnight when our side of Earth has rotated into the direction of the debris trail. A good analogy is this: When driving on a warm summer evening, your car's windshield becomes more bug splattered than the rear window does. Similarly, after midnight, we stargazers are looking through the "front windshield."

CELESTIAL HUGS

Meanwhile this week, the very thin crescent moon will have close encounters with three planets in the early-morning southeastern sky.

On Monday morning, look for a fairly bright "star" to upper left of the moon. That's Saturn. Using even a small telescope, you will be able to see the planet's ring system.

On Tuesday morning, Venus will be just to the upper left of the moon, and Mercury, not quite as bright as Venus, will be just to the lower left of the moon.

HOLIDAY GIFTS

Do you have an astronomy lover on your gift list?

Here's a not-so-subtle plug for my new book, "Stars: A Month-by-Month Tour of the Constellations" ($12.95, adventurepublications.net). This paperback includes anecdotes and simple instructions. I also recorded some commentary that is available as an optional mp3 download.

If you're determined to buy a telescope for that lucky recipient, here's my advice:

-- Avoid department stores. Shop at a reputable store, such as Radio City Astronomy in Mounds View; radioinc.com, where you can talk to experts.

-- To get the most bang for your buck, consider a Dobsonian reflector telescope. You can get one with an 8-inch mirror for less than $600 that will give you wonderful views. (For younger stargazers, you can get a smaller and less expensive version.)

-- The best brands are Meade, Celestron and Orion. Meade and Celestron scopes can be found online at telescopes.com; Orion telescopes are available at oriontelescopes.com.

-- For more info about purchasing telescopes for all ages, check out my website, lynchandthestars.com.

Mike Lynch is an amateur astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis/ St. Paul. Write to him at mikewlynch@comcast.net.